This invention relates to the field of non-destructive magnetic probe testing and more particularly to an eddy-current probe and methods for using it for non-destructive testing of metallic objects, for example plates, and in particular, for example, aluminum aircraft skin.
The need and demand for inspection of metallic plates in an aging infrastructure has been increasing within the last decade due to an increase in both public awareness and concern for the environment. The non-destructive evaluation (xe2x80x9cNDExe2x80x9d) techniques currently in use do not meet all the requirements for such inspections. Recent market research indicates that there is a call for better inspection techniques.
One NDE technique is described in U.S. Pat. No. 6,002,251, which issued Dec. 14, 1999 to Yushi Sun, entitled xe2x80x9cELECTROMAGNETIC-FIELD-FOCUSING REMOTE-FIELD EDDY-CURRENT PROBE SYSTEM AND METHOD FOR INSPECTING ANOMALIES IN CONDUCTING PLATES,xe2x80x9d which is incorporated herein by reference. Dr. Sun""s patent describes a remote-field eddy-current (RFEC) inspection technique and apparatus. The probes described do not provide amplification in the probe.
Magnetic fields create eddy currents within metallic objects in their path. The eddy currents in turn affect the magnetic field. Cracks, discontinuities, holes, and changes in the material content all affect the eddy current flow within the object, and thus the magnetic field external to the object. Remote-field eddy-current techniques generally involve detecting magnetic-field changes remote from the excitation source (often, wherein the magnetic field passes twice through the object), while near-field eddy-current techniques generally involve detecting magnetic-field changes next to the excitation source.
Users desire probes and techniques that are fast, reliable, accurate, easy to operate, and inexpensive. There is a need to extend the RFEC technique, as well as other eddy-current techniques for better noise control and small-flaw detection for inspection of various objects with different geometries, for example, those with flat geometry, or with approximately flat geometry in at least a local area, as well as objects with other surface geometries.
The present invention provides devices and methods for improved inspections of conducting objects, such as flat-shaped conducting structures, as well as conducting structures having other different shapes.
One aspect of the present invention provides a method of transducing magnetic signals indicative of a flaw in a metal object. This method includes shielding an excitation coil on substantially all sides except an emission face, transmitting an alternating magnetic signal to the metal object from the shielded excitation coil, such that the alternating magnetic signal is modified by the metal object, shielding a magnetic detector within a probe on substantially all sides except a reception face. The method also includes receiving the alternating magnetic signal as modified by the metal object into the shielded magnetic detector, converting the received alternating magnetic signal into a first electrical signal within the shielded magnetic detector, shielding a signal-conditioning circuit within the probe on substantially all sides, providing electrical power to the shielded signal-conditioning circuit within the probe, amplifying the first electrical signal with the signal-conditioning circuit to create a second electrical signal, and analyzing phase and amplitude components of the second electrical signal to provide an indication of the flaw.
Another aspect of the present invention provides an eddy-current probe system for detecting a flaw in a metal object. The probe includes an excitation coil unit, a magnetic detector within the probe, a signal-conditioning circuit within the probe, and a signal channel. The excitation coil unit is shielded on substantially all sides except an emission face that transmits an alternating magnetic signal to the metal object, such that the alternating magnetic signal is modified by the metal object. The magnetic detector within the probe is also shielded on substantially all sides except a reception face, such that the alternating magnetic signal as modified by the metal object is received into the shielded magnetic detector and converted into a first electrical signal. The signal-conditioning circuit within the probe is shielded on substantially all sides and provided with electrical power. This circuit amplifies the first electrical signal to create a second electrical signal. The signal channel then transmits the second electrical signal to an instrument for analyzing phase and amplitude components of the second electrical signal to provide an indication of the flaw.
Another aspect of the present invention provides an eddy-current probe system for detecting a flaw in a metal object. This the probe includes an excitation coil unit within the probe shielded on substantially all sides except an emission face that transmits an alternating magnetic signal to the metal object, such that the alternating magnetic signal is modified by the metal object, a magnetic detector within the probe shielded on substantially all sides except a reception face, that receives the alternating magnetic signal as modified by the metal object, and generates a first electrical signal, and shielded means within the probe, powered by an external electrical supply, for amplifying the first electrical signal.
Another aspect of the present invention provides an eddy current system capable of providing multiple phase excitation to an eddy current or a remote-field eddy-current probe. The invention also provides various excitation field forms to enhance sensitivity of these techniques to flaws of different orientations and to increase signal image resolutions. In some embodiments, a multiple-phase excitation generates traveling magnetic fields or rotating magnetic fields on an object. Those fields may have a varying direction in an excitation cycle and high scanning speed at the inspected objects without involving any mechanical movement, hence provide sensitivity to a flaw of any orientations and small pitch of signal data.